This invention relates generally to systems and methods for leak detection in industrial applications, and more particularly to systems and methods for adapting mass spectrometry for leak detection in industrial high production applications.
In high production industrial systems such as, for example, refrigeration heat exchangers, power plants and missile piping, rapid and highly precise leak detection is necessary to insure system quality and safety. Many known leak detection systems employ the technique of helium mass spectrometry for detecting leaks and quantifying the rate of leakage. Typical leak detection systems using mass spectrometry use one of three known techniques.
The first technique is helium sniffing wherein a part under test is pressurized with helium and the environment surrounding the part monitored with a helium mass spectrometer probe. Some of the helium leaking through the part is captured in a gas sample by the probe and conducted to the mass spectrometer. The mass spectrometer then provides a quantitative value of the helium in the sample conducted to the mass spectrometer. However, this procedure produces a qualitative assessment of the leakage rate of the part under test because not all of the helium leaking from the part is conducted to the mass spectrometer. Nevertheless, with practice, an experienced operator can obtain results which parallel quantitative methods.
The second technique also involves pressurizing the part under test to with helium. However, the helium effluent, or leakage, escapes from the part to a closed container and the part can thus be pressurized to operating pressure. When the system reaches equilibrium, the environment of the closed container is then evacuated with a mass spectrometer and the effluent gas analyzed for helium content. Thus, all helium leaking from the part at equilibrium is captured by the system and analyzed by the mass spectrometer, so that the technique provides a quantitative assessment of the part leakage rate. Because the part can be pressurized to operating pressure, this technique provides the most accurate method of leak detection.
The third technique involves internally evacuating the part under test with the mass spectrometer while flooding a closed environment outside the part under test with helium. The mass spectrometer then measures the quantity of helium leaking into the part as a result of the pressure differential between the inside and outside of the part. This technique also provides a quantitative evaluation of the part leakage rate. The test results can be accurate when the part and test system are well calibrated to compensate for the pressure differential and the direction of leakage flow.
However, the use of mass spectrometry renders the leak detection process slow, and also requires a high level of skill from the operator. Furthermore, the technique is difficult to adapt to multiple sampling ports. In particular, the sampling chambers or test ports are often located at significant distances from the mass spectrometer itself. The increased time required for the gas sample to travel the distance to the mass spectrometer adversely affects the accuracy of the test results and decreases the sampling rate. In addition, sample gas frequently accumulates around the sampling port, thus rendering the sample inaccurate. Sometimes, a large bolus of helium from a part with excessive leakage reaches and then saturates the mass spectrometer, which will not be able to sample until cleared of the excess helium gas. This operation frequently takes several minutes to accomplish.
It would therefore be desirable to provide more rapid and high precision systems and methods adapting helium mass spectrometry for leak detection in industrial high production applications using multiple sampling ports. It would also be desirable to provide such systems and methods which reduce the skill level required of an operator. It would be further desirable to provide such systems and methods which reduce the occurrence of saturation of the mass spectrometer with helium gas. It would be still further desirable to provide such systems and methods which reduce flow problems at the sampling ports, so that the gas sample at the sampling port is always representative of the leakage. It would be yet still further desirable to provide such systems and methods which reduce test response time.
These and other objects are attained by a high precision system for adapting mass spectrometry for leak detection in industrial high production applications. In one embodiment the system includes a plurality of sampling ports and a background port coupled to a console including a process controller. The console further includes a vacuum maintenance manifold and a separate sampling manifold to which the plurality of sampling ports and the background port are coupled through sampling port selection valves. The console further includes a helium mass spectrometer with calibrated leak inputs, vacuum maintenance pump, and nitrogen purge supply. The separate vacuum maintenance manifold allows a constant flow from the gas sampling ports to the console, while the calibrated leak inputs to the sampling manifold allow in process calibration and the nitrogen purge prevents saturation of the mass spectrometer with helium from a tested part having excessive leakage.
In another aspect, the invention relates to methods for high precision leak detection in high production industrial applications using helium mass spectrometry. In one embodiment the method includes the steps of using the leak detection system, including the steps of evacuating a test chamber containing parts under test, pressurizing the parts to operating pressure with helium gas, purging the system with a continuous flow of an inert gas, obtaining a sample of gas from the test chamber, and sending the gas sample to a helium mass spectrometer to determine an amount of helium in the gas sample.
The systems and methods provide improved adaptations of helium mass spectrometry for leak detection to industrial high production applications which have multiple sampling ports. The systems and methods allow for more rapid leak detection by facilitating sampling from multiple sample ports. Further, the systems and methods reduce the skill level required of an operator by reducing saturation of the mass spectrometer and by reducing sampling error introduced by flow problems at the sampling ports. In addition, the systems and methods improve the precision of test results by improving sample accuracy.